The present invention relates to transmission link testing, and more particularly to a measuring device for the interface of a transmission link with full-duplex transmission in two-wire common band operation.
It is known (for example from U.S. Pat. No. 4,989,202) that an ISDN (Integrated Services Digital Network) transmission link has a U interface between the transmission line and a so called network. It is further known (cf. "Siemens-KMT-Report, No. 14, order no. E 80001-V331-W54, pages 6 and 7) to perform measurements on this U interface and to provide a corresponding measuring device for this purpose. This measuring device may be used to perform frequency-dependent measurements, functional tests as well as jitter measurements for example. An ISDN transmission link is a special form of a transmission link with full-duplex transmission in two-wire common band operation.
Furthermore, German patent specification DE 44 23 333 C1 discloses a measuring device for the interface of a transmission link with full-duplex transmission in two-wire common band operation. Connected to said interface are a large-scale integrated interface module, via a hybrid circuit and a transformer, on the one hand, and a line termination or a network termination as the test object on the other hand. The measuring device includes means simulating the arrangement of hybrid circuit, transformer and line or network termination, the input of said simulating means being connected to the transmission outputs of the interface module via a high-impedance differential amplifier and the output of said simulating means being connected to an input of a subtractor via a further high-impedance differential amplifier. A further input of the subtractor is connected to said interface via an additional high-impedance differential amplifier; the output of the subtractor communicates with a measuring system.
The invention is based on a measuring device of this type and it is the object of the invention to permit jitter measurements to be precisely performed on the interface of a transmission link with full-duplex transmission during the ongoing transmission using a conventional jitter measuring device.